I thought I'd see if there are any new contestants for an omniwheel, and there's this one I haven't seen before that showed up at the top of the list:

In the listing, there were 3 similar wheels that looked really cool, and for some reason, the darker it became the more it could carry.

It's twice the price I'd like to pay for a wheel, but I get 2 wheels so...

Anyway, as it turns out, the different colours are because of the different hardness levels:

Considering that the other wheels I was going to go for were heavier and only held 40kg, any one of these seems like a win. Looking at research such as [this] and [this], it seems that the harder the wheel, the easier it is to slide across surfaces, particularly hard ones. The outdoors is predominantly hard surfaces, though it's rough and hard. I may want some vibration damping found in the 60A and 85A options. 

I think the 85A option has the best balance between aesthetics, sliding ability, durability and potentially vibration damping, though I can see why the seller recommends the 60A. The additional dampening and low noise could be beneficial.

While reading this mechasuit project log, I saw this:

This is the kind of thing I need to actuate the omniwheel. This would be used along these components:

Honestly, I only need 2 linear rails and one 300-500mm long stick, but for consistency (and because I can't find a 1pc listing) I'm going to use an empty 3rd HGR rail for the 2nd stage. The entire weight should be in the ballpark of 2.5kg, though the lengths required are subject to change since I don't yet know if it'll all fit in a 600mm tall backpack.

HGR15 has a cross section of 15*15mm, which should be enough to hold the weight of a packed backpack. There are likely cheaper ways of going about this, but the width of this needs to be as low as possible to prevent collisions with legs and maximise space available inside the backpack. I have more confidence in an otherwise unsupported HGR15 rail compared to an MGN12/15, with my concerns mainly being around the bearing static load.

For actually holding the actuator in the fully extended or fully closed state, I'm thinking of a servo connected to a small suspension spring, similar to the ones I found for #TEOSS [gd0037] a while back.

Oh. 450lb? Those are much too strong. 

Seems like gas springs are what I'm actually looking for. 

Whilst walking around the past few days, I've been mentally simulating having a backpack with varying amounts of features that are implemented in various ways. I think I've made my simple and inescapable choice: pogo wheel. 

The enter-bag-without-dismount feature seems to add quite a bit of complexity for a situation that relatively happens for a small percentage of time using this imaginary backpack. 

By far the biggest net benefit would be to direct the gravitational force of the backpack straight into the floor, without the literal middle man. The suitcase method has usability challenges, mainly caused by sharp changing elevation requirements (curbs, steps), the payloads would be subject to additional impacts, increasing the risk of damage, and it is unlikely that lifting the entire compartment when switching between wheeled and suspension modes is a simple engineering challenge. 

Compared to this, the pogo-stick wheel is lighter (requiring less power to extend and retract, as well as a fixed weight) and smaller, reducing the likelihood of my feet colliding with anything when moving.

For true manoeuvrability, a 2 directional (normally called an omnidirectional) wheel will be required. To cut down on noise and to ensure compatibility with #TEOSS [gd0037], a wheel with a diameter larger than 100mm is probably a good idea. In research, it seems that wheels that size and up would be needed anyway to support the weight of the bag. I didn't look into it much, but it seems that the swivelling trolley wheels, diameter being equal, is only slightly cheaper. Since these wheels can't roll in different directions instantaneously and the chance of a foot collision is higher, I've decided to skip them.

Currently, I think the features in order of importance is:

1. Can safely carry #Teti [gd0022].
2. Retractable pogo-stick wheel that is safe to use with TEOSS.
3. Soft, rolling straps.
4. Hoverglide suspension.

Wheels I found yesterday:

First thing I saw was this really expensive wheel with a really expensive shipping cost. I think it's for a really expensive mobility scooter. The description says it's 3.7kg so that's out.

This wheel can take 30kg of force and weighs 360g or something, but it also costs more than any backpack I've ever bought. I knew this backpack was going to be much more expensive than whatever I could buy off Amazon/AliExpress, but...

This one is 320g and can do 20kg, but I probably shouldn't try this wheel is when going at elevated speeds. Then again, I just remembered that some kick scooter wheels have plastic rims, so perhaps it's fine:

Now if I'm spending the big bucks, might as well go with the platinum skin. I've got no idea of the durability of this wheel or if said wheel would actually damage the ground, but metal wheels have less friction and this application calls for such low friction wheels. This wheel looks beautiful and I'm currently using this design for all mental conceptural imagery, but apparently it can only carry a measly 5kg. Why? It's also 539g (though most other listings state 250g). I once found a larger 127mm wheel that was essentially £135 considering VAT and could allegedly carry 20kg, but I have even less faith that aluminium would last.

Then there's this 740g wheel that can carry 40kg:

I do wonder if the alternating wheels for all but the "platinum skin" one would cause any usability of safetly issues.

[Published 18:00, 8th Dec 2022]

The past week or two, I've been trying to recompute a solution. The tough part of all of this is that this project is more of an optimisation problem instead of creating something that just doesn't exist. Well, some features I'd like to incorporate do exist but only in rare circumstances. This log might be a bit hectic; it's the first log that has taken me multiple days to write.

First, the shape

Anyway, the first thing I've been thinking of is the shape. Up until the past 28 days or so, I've been thinking that the second concept idea would be a square prizm, but with the #T^2 TyMist [gd0138] being cylindrical now and #TEOSS [gd0037] expected to be redesigned with a slot-like design (I haven't yet modelled it to see if I like it), I was thinking of going with a cylindrical base shape. Coincidentally, the most favourite backpack I've ever owned (but was short lived because the strap broke) was this cylindrical backpack:

Back in late 2018, I planned to buy some copper PETG and print an internal frame so that it was always cylindrical like in the images. Well I never got around to that and now I've learned that it's best to design in CAD before buying a £63 roll of Extrudr PETG. I've only used like half a metre of this massive 30cm roll, and it was a reason why many of my current projects have copper accents. 

I also wanted to put a low cost tablet to show animations on that bag. With this project, I'm thinking of going with a strip of LED matrix panels.

Groceries?

I've also been thinking of ways that the backpack could carry my singular extra large "Bag For Life" supermarket grocery bag, and thought about "cutting the middleman", which in this case is making the backpack also the shopping bag. I looked on google and it turns out I'm essentially trying to make a "shopping trolley" that has the rigidity of a suitcase, the suspension of a hoverglide and a body harness with a grappling lift (which I'll write about later).

I knew I should've written this log earlier, because whilst looking for the above example image, I found out that even getting over curbs and steps is a solved problem:

Problems to solve

Now, other than the squishiness of regular backpacks and anti-curb nature of suitcases, there are a few other issues I want to solve:

1. Quickly putting the backpack on, including the hip strap.
2. Improve softness of the straps.
   1. I believe 1 and 2 can be solved with a soft cylindrical tube that is able to freely rotate. The strap will always be facing the "correct" way when put on (eliminating the time spent readjusting) and the increased padding will subsequently increase softness and comfort.
3. Be able to lower the bag onto the floor and use it without needing to take the strapped section off.
   1. This might seem to not be needed if cylindrical straps are used, but even then, that doesn't solve the issue of having both hands holding a larger item and needing to access the backpack. The arms have to go through the strap to take it off, requiring the user to put down whatever may be knocked out by / can't fit through the straps.
4. When rolled, not needing to use a hand to pull. It also needs to be TEOSS compatible.
   1. That way, it'll be like a backpack but most of the gravitational force is exerted into the ground and not my skeleton. 
   2. I can't choose a solution that only works at walking speed but become an unpredictable hazard at 25km/h (target TEOSS speed). I'd only be going at that speed on long, straight sections, so it's not like it needs to be able to corner and take curbs at elevated speeds. 
5. Eliminate zippers
6. Carry always-up items (like drinks with whipped cream on top) safely.
7. Removable compartment
   1. This is to be able to reconfigure the bag based on the required use case.

Cylinder concerns

One of the reasons I didn't want to go with a cylinder was because #Teti [gd0022] isn't and I expected the diameter to be rather large. It's actually prretty close to TyMist's diameter, so I might actually have Tetinventory use the same diameter as TyMist:

Now the thing is that a 360mm backpack is quite large. It's probably a fine amount of space for groceries though. 

First round of ideas

Space Lift idea

I was thinking of having tether cables over on one semi-circle side to achieve feature [lower/raise bag from floor] until I eventually remembered that the bag would be raised from the centre of gravity, which will likely mean that the bag will hit my legs. Now, if this impact is nice and slow and ordered, I don't imagine this being a problem. 

There's still another problem which is that the bag now may not be aligned to the suspension rails (the thing that the bag will slide on whilst bobbing up and down). I might have to add some extra sections around the main bag to be able to go with this "space lift" idea, having 4 cables roughly equidistant. A possible issue with this idea is the cables getting twisted, leading to chaotic behaviour.

Wasp Bot idea

I was also thinking of a relatively tall bag such that it could be lowered and the wheels would be in contact with the ground whilst the top of the cylinder is in contact with the bottom of the strap half. I'd imagine I would look vaguely like a humanoid robotic wasp. I have a feeling that the bag would have to be quite tall to work.

Pogo Wheel idea

Another idea was to have a pogo-like stick with a wheel at the bottom so that the cylinder can be at normal backpack height.

With those inital thoughts, I decided to explore the cable method more since I belive that the [hoverglide suspension], [no-hands suitcase rolling] and [bag entry without dismounting] features can all be solved with the same system.

Second round of ideas

Multidirectional Wheels idea

Since my compartment choices are between an extruded square or circle, I'm thinking of adding enough wheels to make the compartment orientation agnostic when rolled. When cornering too sharply or hitting a curb too quickly, my wheeled backpack can obtain angular momentum and tip over to a side. Since the thing connecting the straps to the compartment needs to be flexible for the [bag entry without dismounting] feature, I'm expecting unexpected rotations to occur often.

This idea requires that whatever is holding the compartment to the straps is either connected to the top centre or rotates around the centre.

Rope that can switch from flexible to stiff

It seems [suitcase rolling] and [bag entry without dismounting] require different attachment methods for the compartment. For suitcase rolling, the object connecting the stap-half to the compartment-half needs to be rigid except for a single hinge point, similar to the hinge between a trailer and truck. However, there's no possible way of getting into the bag unless the object can flex so that I can turn around and open the bag. The object also needs to be stowable for when the compartment is in [hoverglide suspension] mode

What I need is some kind of artificial rope that can switch from stiff to flexible. I'm fine with requiring that the rope is straightened out before being stiffened. Additionally, it only has to be stiff enough that the compartment section doesn't roll straight into my legs when I'm going down a hill or just slowing down.

I've learned from this project log from Detail that there exists a fluid that can change viscosity in the presence of a magnetic field. I'm not sure if I could install an electromagnet across an entire hose that contains this fluid, nor do I know how expensive the fluid is. 

My current idea is a set of 3D printed linkages that has 2 wires going through them all. Those are power wires for low cost solenoids (or maybe servos) that will allow a spring-loaded shaft to slot into a hole, preventing the linkages from rotating and essentially turning a flexible chain into a rigid one.

Depending on how quiet and light a suitable pump is, it may also be possible to pressurise a hose to stiffen it, similar to an airbed.

This log continues from the one from Teti.

So this was the idea I've had in my mind for months on how it would look like. I was modelling yesterday night and I thought it looked kind of plain so I added copper brackets to the side. Looking at it after sleeping, this concept looks fresh and minimalistic.

Anyway, it looked a lot more backpack-like. 

First I tried out a design where the kelvinA logo is centered at the bottom of the face and the top line of the T.

I then tried the more... lawful branding design, as well as extending the brackets and adding the gyro ball cup holder. Added some feet and rendered the design:

After sleeping and waking up, the second back panel idea seems more dull (likely because it's more predictable) and one-sided than the first idea. Additionally, I wonder how the design will progress with the addition of the suspension rails and methods of entry into the bag without standard things like buttons or zippers. I also would like to be able to deploy a motorised helmet for portable AC-ed air around my face (likely to be branded under the SludgeCo project) and have some kind of exoskeleton legs that attach to TEOSS to take some force off my body, but that's somewhat far thinking and I mainly just need to focus on the main features for now.

This is the Log Entry that will be dedicated to tracking any and all project name changes.

Current Changes

• [5 April 2022] Tetinventory (possible short name: Tet-INV)
• [Project start] KabanChan 
  • Currently the backpack project's internal name, named after the character from Kemono Friends